Initialize some global variables in Bitmap.cpp when needed

Bug: 331243037
Flag: EXEMPT bugfix

This allows Bitmap class to have a static NativeAllocationRegistry,
which can be used to register native allocations of different sizes
without creating multiple registries.

To make this possible, the static native method nativeGetNativeFinalizer
needs to be available during static initialization time in Bitmap class.
However, there is a deadlock as shown below which needs to be removed

e.g.

class Bitmap {

  private static long sFinalizer = nativeGetNativeFinalizer();

  private static native long nativeGetNativeFinalizer();
}

The static initialization of sFinalizer depends on the native JNI call
nativeGetNativeFinalizer() to be available/registered. However, during
JNI registration time in Bitmap.cpp, the calls of GetMethodID() requires
the static initialization to be done, this causes deadlock, and hence
the code above wouldn't work.

To remove this deadlock and thus allow static native methods to be
called during static initialization, we moved the initialization of
these global variables in Bitmap.cpp, which depends on GetMethodID(),
to be done later when they are needed first time.

Change-Id: I87bebdbe128a2dad48b162d31ed275ad7908bcd7